In many industries and particularly in the pressing of oil from vegetable matter, it is common practice to make use of worm or screw presses which can have a generally cylindrical chamber formed in an elongated housing which may be provided with heating and/or cooling means, and a worm rotatable in this housing and provided with at least one and preferably a plurality of helical ribs or flights which are capable of displacing material from an inlet end of the passage to the discharge ends thereof while masticating, plastifying, compressing and frictionally treating the material.
For example, the worm may be defined axially into a plurality of sections with different flight pitches, root diameters or numbers of helical flights or ribs, thereby ensuring axial compression as the material is forced past a discharge constriction at the end of the passage. The relative movement between the mass of material and the flights for other portions of the worm and between the mass and the walls of the chamber, subject the material to shearing action which assists in homogenizing the mass.
The housing or cylindrical shell may be heated, e.g. by heating jackets and heating fluids or electrical heating means, if the compression, mastication and homogenization is to be accompanied by a heat treatment. The shell can be provided with passages, coils or the like, traversed by a coolant if sensitive materials are to be treated and the friction heat and compression heat must be abstracted.
It has been found to be advantageous, when such presses are used for the pressing of vegetable matter and for solid/liquid separation, e.g. as is the case in the pressing of oil for vegetable matter, to provide one or mre constrictions along the path of the material from one end of the passage to the other.
Therefore each constriction is conventionally formed by a ring mounted on the housing and having an inwardly turned frustoconical flight which confronts an outwardly directed frustoconical flank on an annular shoulder of the worm.
A worm press of the aforedescribed type is illustrated and discussed in German patent document No. 1,944,642 which indicates that the adjustability of the constriction gap can be a function of relative axial displacement of the two members, i.e. the ring or the shoulder forming this gap.
In this system, the housing and the worm are both axially fixed and the adjustability is provided by mounting the worm so that it can be displaced axially by an appropriate drive mechanism, on the housing.
With this system however, a problem arises with respect to sealing the passage in the region of the axially displaceable ring under the high pressures which may be generated in the pressing passage.
Even with the best of seals known to date, some discharge past the seals unavoidably occurs.
The constriction of this arrangement is expensive, is frequently unreliable and requires high maintenance costs.